For what it's worth, I rushed yesterday (not the weekend, but hopefully a helpful indication of what you want to know). I got there at about 8:50, and I was maybe 5th or 6th in line. I had no problem getting tickets. By 10:00, I would estimate that there were roughly 15 people total.
Because you want the matinee, it should be easier for you to get tix, but if you want to be safe, I would not recommend getting there after 9. Since it's the final weekend, maybe get there at 8:15-8:30 if you want to be very safe? Just an estimate. Hard to know for sure.